1. Field of the Invention
The present invention relates to a new, safe, effective method to neutralize or destroy a wide range of airborne pathogens (spores, bacteria and viruses) in commercial HVAC air handling systems.
2. Description of the Related Art
It is critical to develop rapid, effective, and safe (nontoxic and noncorrosive) pathogen neutralization technologies to protect civilian and military facilities from a chemical or biological attack. Within this area, emphasis is on the pathogen neutralization of domed stadiums, subways, and enclosed facilities (buildings and command centers that may contain extremely sensitive equipment. This effort is a key to eliminate the threat of biological weapons in the planning and conduct of US military operations. While no defense can stop an adversary from unleashing biological weapons, a sufficiently robust array of pathogen defenses and countermeasures-deterrents will reduce the damage resulting from biological weapons used in a particular operation.
There is also a great need to remove airborne pathogens form air handling systems in hospitals where the transmission of respiratory infections in indoor environments represents a major public health concern for which engineering alternatives are limited. Evidence for the dissemination of respiratory diseases inside buildings, and specifically by ventilation systems, exists in the epidemiological data. The risk to patients of becoming infected with Staphylococcus, one of the most common and deadly infections associated with prolonged hospital stay, is significant.
To accomplish these goals, a pathogen neutralization technology is needed that can destroy a wide range of pathogens (spores, bacteria, and viruses) in air in real time as it moves through an HVAC system without introducing contamination into the air handling system. The neutralization system of airborne biological pathogens is a very difficult problem to solve because many of the agents are highly resistant to traditional neutralization methods that have thus far been primarily useful to disinfect surfaces. Therefore, an aggressive neutralization approach is required.
Ozone is a highly effective disinfectant in water and on surfaces, but the use of ozone as a disinfectant to neutralize pathogens in air has not been demonstrated before. Ozone is the second most powerful oxidant and sterilant (fluorine is first) used in the destruction of bacteria and viruses. The threshold concentration at which ozone inactivates viruses and bacteria in water is low.
Ozone gas is extremely effective for controlling bacteria and virus contamination. It has been used quite successfully and safely in Europe for the purification of drinking and recreational water since the 1800's. It is fast becoming a replacement for chlorine and bromine, which have been shown to be carcinogenic. However, to date, no commercial HVAC system have been developed that uses ozone to disinfect airborne pathogens.
Ultraviolet (UV) light is reemerging as an alternative disinfectant to chlorination because of concern over toxic chemical byproducts. UV radiation treatment is unique in its mode of action, in that it does not necessarily kill the target microorganism. Instead, the UV radiation damages the DNA in the pathogen so that it cannot reproduce. Treating water with ozone bubbling through it, followed by UV irradiation (U.S. Pat. Nos. 4,156,652, 652, 4,179,616, 4,204, 4,230,571) has been shown to be an effective method of neutralizing waterborne pathogens. However, all of these systems depend on dissolving ozone in water to destroy the pathogens. The ozone intermediate free radicals formed by the interaction of ozone with water in the presence of UV light, act as oxidants on cell walls even before they penetrate inside the microorganisms where they oxidize essential components such as enzymes and proteins.
It has been reported that ozone itself does not react significantly with either water or air in the absence of UV irradiation. Water and air merely provide the medium in which ozone diffuses to react with organic molecules such as those on the outside of the pathogens in the cell wall. UV irradiation causes ozone to react with water and to decompose into various highly active and very short-lived free radicals, such as the hydroxyl radical. Theoretical and empirical evidence suggests that it is the interaction of the pathogen with the free radicals, and not with the ozone itself that is responsible for most pathogen neutralization. NIST Report “Photoinitiated Ozone-Water Reaction”, J. Res. NIST, 97:499 (1992).
So far there is no effective way to disinfect or neutralize airborne pathogens in large volumes of contaminated air in real time to protect citizens against a terrorist attack using biological weapons, or to disinfect air in hospitals. The present invention provides such an apparatus and method for neutralizing airborne pathogens.